Williams back to her best against Sharapova

Serena Williams sent out an ominous message to the women's game as she stormed past Maria Sharapova, booking her place in the semi-finals of the Bank of the West Classic for the loss of just four games.

The American, down to 169 in the world following a year of injury and health problems, was close to her powerful best as she raced to a 6-1 6-3 win over the Wimbledon finalist and second seed in 69 minutes.

Williams was dominant on her own delivery, winning 75% of points on her first serve, as she followed up her wins against Maria Kirilenko and Anastasia Rodionova, who she beat 6-0 6-0 in the first round.

Williams' semi-final will be a seed-free affair after Sabine Lisicki dumped out Agnieszka Radwanska.

The fifth seed slipped to a 7-6 (7/4) 2-6 6-2 defeat.

The other semi-final will be between the third and eighth seeds after Marion Bartoli advanced thanks to Ayumi Morita's retirement and Dominika Cibulkova eased past qualifier Marina Erakovic 6-1 6-1.